The purposes of this project are to examine the contributions of central motor programming and afferent input in control of arm movements in normal subjects and patients with sensori-motor disorders, and to study psychomotor performance of patients with central motor disorders. The first set of experiments records muscle activity and kinematics of lim position while (1) subjects manually match a target display with either a skilled rapid or slow movement with a handle whose displacement controls a visual display or (2) maintain postures when limb position is passively changed. Movement amplitude, presence or absence of visual feedback of position, disturbances of the subject's movements and changes in sensory input are independent variables. Large movements are performed accurately independent of manipulation of the experimental variables but accurate performance of small movements becomes increasingly dependent on the absence of limb disturbances during movement. The second set of studies examined a variety of psychomotor variables from patients with Parkinson's disease. The relationships between movement speed, movement accuracy, target size and movement amplitude were studied to develop sensitive measures of psychomotor performance that correlated with clinically determined fluctuations in drug efficacy.